Target tracking using surface scanner and four-dimensional diagnostic imaging data

ABSTRACT

Tracking a pathological anatomy within a patient&#39;s body is described. A data model of a skin surface of the patient&#39;s body may be acquired using light reflected from the skin surface. The data model can be matched with skin surfaces reconstructed and/or interpolated from four-dimensional diagnostic imaging data, such as 4D CT data, to determine a temporal phase of the patient&#39;s respiratory motion. The identified temporal phase may then be used in conjunction with the diagnostic imaging data to identify a location of the pathological anatomy within the patient&#39;s body.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/008,083 filed Jan. 7, 2008.

TECHNICAL FIELD

This invention relates to the field of radiation treatment, and inparticular, to a system of tracking the movement of a pathologicalanatomy during respiration.

BACKGROUND

One challenge facing the delivery of radiation to treat pathologicalanatomies such as tumors or lesions is identifying the location of thetarget (i.e. tumor location within a patient). The most common techniquecurrently used to identify and target a tumor location for treatmentinvolves a diagnostic x-ray or fluoroscopy system to image the patient'sbody to detect the position of the tumor. This technique assumes thatthe tumor is stationary. Even if a patient is kept motionless, radiationtreatment requires additional methods to account for movement due torespiration, in particular when treating a tumor located near the lungs.Breath hold and respiratory gating are two primary methods used tocompensate for target movement during respiration while a patient isreceiving conventional radiation treatments.

Breath hold requires the patient to hold his or her breath at the samepoint in the breathing cycle and only treats the tumor when the tumor isstationary. A respirometer is often used to measure the tidal volume andensure the breath is being held at the same location in the breathingcycle during each irradiation. This method takes longer than a standardtreatment and often requires training the patient to hold his or herbreath in a repeatable manner.

Respiratory gating is the process of turning on the radiation beam as afunction of a patient's breathing cycle. When using a respiratory gatingtechnique, treatment is synchronized to the individual's breathingpattern, limiting the radiation beam delivery to only one specific partof the breathing cycle and targeting the tumor only when it is in theoptimum range. This treatment method may be much quicker than the breathhold method but requires the patient to have many sessions of trainingto breathe in the same manner for long periods of time. This trainingrequires many days of practice before treatment can begin. This systemmay also require healthy tissue to be irradiated before and after thetumor passes into view to ensure complete coverage of the tumor. Thiscan add an additional margin of 5-10 mm on top of the margin normallyused during treatment.

Attempts have been made to avoid the burdens placed on a patient frombreath hold and respiratory gating techniques. In another method totrack the movement of a tumor in real time during respiration, acombination of internal imaging markers and external position markershas been used to detect the movement of a tumor. In particular, fiducialmarkers are placed near a tumor to monitor the tumor location. Theposition of the fiducial markers is coordinated with the externalposition markers to track the movement of the tumor during respiration.External position markers are used because the fiducial markers aretypically monitored with x-ray imaging. Because it may be unsafe toexpose the patient continuously to x-rays to monitor the fiducials, theposition of the markers can be used to predict the position of thefiducial markers between the longer periods of x-ray images. One type ofexternal position markers integrates light emitting diodes (LEDs) into avest that is worn by the patient. The flashing LEDs are then detected bya camera system to track movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1A illustrates a system for tracking motion of a target within thebody of a patient and delivering treatment to the tracked target.

FIG. 1B is a flow chart illustrating a process of preparing for anddelivering radiation treatment while tracking motion of a treatmenttarget.

FIG. 2 is a flow chart illustrating a pre-treatment preparation processfor radiation treatment using a treatment delivery system having motiontracking capabilities.

FIG. 3 is a flow chart illustrating stages in a treatment delivery phaseusing a treatment delivery system having motion tracking capabilities.

FIG. 4A is a flow chart illustrating stages in a process for acquiring adata model of a skin surface.

FIG. 4B is a block diagram illustrating components of a digitalphotogrammetry system.

FIG. 4C is a block diagram illustrating components of a laser scanningsystem.

FIG. 5A is a flow chart illustrating stages in a process for registeringa data model of a skin surface with four-dimensional computed tomography(4D CT) data.

FIG. 5B illustrates a process for registering an acquired skin surfacewith surfaces reconstructed from 4D CT data.

FIG. 6A is a flow chart illustrating stages in a process for registeringa data model of a skin surface with four-dimensional computed tomographydata.

FIG. 6B illustrates a process for registering an acquired skin surfacewith surfaces reconstructed from 4D CT data.

FIG. 7 illustrates a process for determining a tumor position relativeto a skin surface by interpolation.

DETAILED DESCRIPTION

Described herein is a method and apparatus for tracking the movement ofa pathological anatomy during respiration. The following descriptionsets forth numerous specific details such as examples of specificsystems, components, methods, and so forth, in order to provide a goodunderstanding of several embodiments of the present invention. It willbe apparent to one skilled in the art, however, that at least someembodiments of the present invention may be practiced without thesespecific details. In other instances, well-known components or methodsare not described in detail or are presented in simple block diagramformat in order to avoid unnecessarily obscuring the present invention.Thus, the specific details set forth are merely exemplary. Particularimplementations may vary from these exemplary details and still becontemplated to be within the spirit and scope of the present invention.

According to an embodiment of the present invention, the motion of apathological anatomy, such as a tumor, within the body of a patient maybe tracked by acquiring a data model of a skin surface of the patient'sbody, then matching the data model with four-dimensional (4D) diagnosticimaging data, such as four-dimensional computed tomography (4D CT) datafrom the patient that includes the location of the pathological anatomyrelative to the skin surface. During radiation treatment of the patient,the data model may be acquired by capturing light reflected from thesurface of the patient's skin. For example, the data model of thepatient's skin surface may be acquired using techniques such as laserscanning or photogrammetry.

According to this process, the data model can be compared with 4Ddiagnostic imaging data from the patient that includes the images of thepathological anatomy in order to track the motion of the pathologicalanatomy. The 4D data may include a series of three-dimensionalrepresentations of the patient's anatomy, each correlated with atemporal phase. The temporal phases may, for example, represent phasesin the patient's respiratory cycle. Each of the three-dimensionalrepresentations of the patient's anatomy may describe the location ofthe pathological anatomy relative to the patient's skin surface. Thedata model of the patient's skin surface may then be matched with one ormore of the three dimensional representations within the 4D diagnosticimaging data in order to determine the location of the pathologicalanatomy at the time the data model of the skin surface was acquired.

FIG. 1A illustrates a system for tracking motion of a pathologicalanatomy, such as a tumor, using four dimensional (4D) diagnostic imagingdata and skin surface acquisition according to one embodiment of theinvention. Treatment delivery system 100 includes processor 101, surfacescanner 102 for acquiring a data model of skin surface 105 of patient106, four dimensional computed tomography (4D CT) data 103, linearaccelerator (LINAC) 104, and robotic arm 108. Motion tracking system canbe used for tracking motion of a target 107 within patient 106, whilethe patient lies on treatment couch 109.

In treatment delivery system 100, processor 101 is connected withsurface scanner 102 so that processor 101 may control operation ofsurface scanner 102 and receive data acquired by surface scanner 102.Surface scanner 102 may be any device capable of acquiring data that canbe used to produce a data model of skin surface 105 of the patient 106.For example, surface scanner 102 may be a laser scanner or a digitalsurface photogrammetry system, such as the Vectra 3D Scanner produced bySurface Imaging International, Ltd. Processor 101 also has access tofour-dimensional computed tomography (4D CT) data 103. 4D CT data 103may have been acquired from a 4D CT scanner. The 4D CT data may bestored on a magnetic disk or other computer-readable medium. Inalternative embodiments, 4D CT data 103 may be replaced with other formsof diagnostic imaging data. For example, 4D CT data 103 may be replacedwith a data model that was acquired by means other than computedtomography. Processor 101 may be further connected to linear accelerator(LINAC) 104, which is capable of producing a radiation beam suitable forradiation treatment. Processor 101 may be connected to LINAC 104 so thatprocessor 101 can control the output and other aspects of operation ofLINAC 104. Processor 101 may also be configured to receive informationfrom LINAC 104, such as status information. LINAC 104 may be mounted ona robotic arm 108 that can be controlled by processor 101. Robotic arm108 may provide processor 101 with the ability to direct the beam ofLINAC 104 at different locations and from different angles.

Surface scanner 102 may be positioned to acquire a data model of skinsurface 105 which lies over target 107. This data model can then betransmitted to processor 101, which compares the data model with 4D CTdata 103. Based on the comparison between the acquired data model and 4DCT data 103, processor 101 determines the position of target 107.Processor 101 can then direct robotic arm 108 to move so that the beamof LINAC 104 intersects target 107. In one embodiment, target 107 is apathological anatomy such as a tumor. Alternatively, target 107 may beany subject for which location tracking is desired. By repeating theprocess of acquiring a data model of skin surface 105, comparing thedata model to 4D CT data 103, determining the location of target 107,then moving robotic arm 108 so that the beam of LINAC 104 intersectswith target 107, processor 101 may track the location of target 107continuously and maintain the beam of LINAC 104 directed at the targetfor the duration of a radiation treatment session, even while the targetis moving.

FIG. 1B is a flowchart illustrating a process of preparing for anddelivering radiation treatment to a target within the body of a patient,while the location of the target is tracked using a system such astreatment delivery system 100, according to one embodiment of theinvention. Radiation treatment process 110 includes pre-treatmentprocess 200, followed by treatment delivery process 240. Pre-treatmentprocess 200 further includes scanner calibration phase 210 and treatmentplanning phase 220, which are followed by patient alignment phase 230.During scanner calibration phase 210, a surface scanner is first mountedin the room where the radiation treatment is to take place, as providedin process block 211. Then, the surface scanner is calibrated withrespect to a treatment couch in the treatment room, as provided inprocess block 212. In the treatment planning phase 220, four dimensionaldiagnostic data, such as 4D CT data, is acquired and loaded into atreatment planning system, as provided in process block 221. In thefollowing block 222, a skin surface of the patient being treated isreconstructed from three-dimensional (3D) diagnostic data derived fromthe 4D diagnostic data. For example, 4D CT data may be considered as aseries of 3D CT images each corresponding to a point in time. The 3D CTimages can then be used to reconstruct the skin surface according toprocess block 222. In process block 223, a tumor within the patient'sbody is segmented, or reconstructed, from the CT data. In block 223, thelocation of the tumor is also determined relative to the skin surface.Following the completion of scanner calibration phase 210 and treatmentplanning phase 220, patient alignment phase 230 may begin. In patientalignment phase 230, the patient is first placed on the treatment couch,as provided in process block 231. Then, in block 232, the CT data isaligned with the treatment couch and the patient. In other words, atransformation is determined that relates the CT data to the patient andthe treatment couch. Pre-treatment process 200 is followed by treatmentdelivery process 240, including surface tracking phase 310, which isfollowed by targeting phase 320. In surface tracking phase 310, a datamodel of the patient's skin surface is captured using the surfacescanner. The skin surface may be in motion at the time of the capture,for example, as a result of the patient's respiratory cycle. In processblock 312, the acquired data model is then registered with skin surfacesreconstructed from the 4D CT data in order to determine a temporal phaseof the patient's respiratory cycle at the time the data model wasacquired. Once block 312 has been completed, targeting phase 320 maybegin. Targeting phase 320 begins with block 321, where the tumorposition is located using the registered skin surfaces and the temporalphase previously determined in block 312. Once the location of the tumorhas been determined, a LINAC may be moved so that its beam intersectsthe tumor. Blocks 311, 312, 321, and 322 of treatment delivery process240 may be repeated so that the beam of the LINAC is continuouslydirected at the tumor for the duration of the treatment delivery process240. Radiation treatment process 110 is described in more detail in thefollowing paragraphs.

FIG. 2 is a flowchart illustrating a pre-treatment process 200 forpreparing a system such as treatment delivery system 100 prior to aradiation treatment session of a patient, according to one embodiment ofthe invention. Pre-treatment process 200 may be part of radiationtreatment process 110, as previously described. Pre-treatment process200 includes three main phases: the scanner calibration phase 210, thetreatment planning phase 220, and the patient alignment phase 230.

During the scanner calibration phase 210, a surface scanner such assurface scanner 102 is mounted in a treatment room. The surface scanner102 may be mounted anywhere in the treatment room, so long as surfacescanner 102 is mounted in an orientation that enables surface scanner102 to acquire a data model of skin surface 105. In one embodiment,surface scanner 102 may be attached to a fixed mount, while in otherembodiments, surface scanner 102 may be attached to a movable mount,such as a tracked robotic mount. After surface scanner 102 is mounted asdescribed in process block 211, the surface scanner 102 is calibratedwith respect to the treatment couch, as described in process block 212.Calibration may be performed by determining the transformation from theimaging plane or the imaging volume of the surface scanner 102 to thetreatment couch 109.

The treatment planning phase 220 may take place before, after, orconcurrently with the scanner calibration phase 210. The treatmentplanning phase 220 begins with process block 221, where 4D CT data ofthe patient to be treated is acquired and loaded into a treatmentplanning system, according to one embodiment of the invention. In otherembodiments, the data may not necessarily be 4D CT data, but may also beany data that describes the subject of the treatment in multipledimensions. For example, the data may be a series of 3D CT scans, or aseries of 3D images obtained by methods other than CT. The 4D CT data isacquired so that it includes the portion of the patient's anatomy towhich treatment will be administered. The 4D CT data includes a threedimensional representation of the patient's anatomy that is capturedover time, so that changes in the patient's anatomy over time are alsocaptured. For example, the shape of the patient's body may change overtime as the patient breathes. These temporal changes corresponding tophases in the patient's respiratory cycle may be captured by the 4D CTscan. After 4D CT data is acquired, the data is loaded into thetreatment planning system. The treatment planning system into which the4D CT data is loaded may be a system that is configured to executetreatment planning phase 220. For example, the treatment planning systemmay be a computer having software installed that executes the stages221, 222, and 223 of treatment planning phase 220. Thus, loading 4D CTdata into the treatment planning system may simply entail making thedata accessible to the treatment planning system on a storage medium,such as an optical or magnetic disk.

After the 4D CT data is loaded into the treatment planning system asprovided in process block 221, execution proceeds to process block 222,where the treatment planning system reconstructs the skin surface of thepatient from the 4D CT data. The 4D CT data may be considered as aseries of three-dimensional (3D) CT images each corresponding to a pointin time. Each of these 3D CT images can then be used to reconstruct skinsurfaces corresponding respectively to those points in time. The pointsin time corresponding to the reconstructed skin surfaces can then beconsidered as temporal phases in the patient's respiratory cycle. Thus,the result of process block 222 is data representing a series ofreconstructed skin surfaces corresponding to temporal phases in thepatient's respiratory cycle.

In process block 223, the tumor within the patient is segmented, orreconstructed, for each temporal phase from the CT data corresponding tothe temporal phase. The reconstructed data model of the tumor is thenrelated with the reconstructed skin surface corresponding to the sametemporal phase. In other words, for each temporal phase, the orientationand position of the tumor with respect to the reconstructed skin surfacefor that temporal phase is determined.

After completion of the scanner calibration phase 210 and the treatmentplanning phase 220, the pre-treatment process 200 continues to thepatient alignment phase 230. The patient alignment phase 230 may beginwith the placement of patient 106 on the treatment couch 109, asprovided in process block 231. Execution then continues to process block232, where initial alignment of the patient is performed. The goal ofprocess block 232 is to determine the appropriate transformationsbetween the acquisition plane (or volume) of the surface scanner and theCT data. In other words, the goal is to align the CT image and surfacescan so that a similarity match can later be determined between them.This goal may be accomplished using landmark-based registration. Forexample, while patient 106 is lying on treatment couch 109, the body ofpatient 106 may contain one or more landmarks such as a spine, otherbones, or implanted fiducials. The locations of the landmarks while thepatient 106 is lying on treatment couch 109 can be resolved using suchtechniques as X-ray or ultrasound. The landmarks also appear in the CTimages. Thus, the CT images and the actual patient 106 can be aligned inthree-dimensional space by matching the locations of the landmarks.Since the patient 106 is stationary with respect to treatment couch 109,the transformation between the CT images and the treatment couch can bedetermined. Then, since the transformation between the treatment couch109 and the acquisition plane or volume of surface scanner 102 hadpreviously been determined in process block 212, the transformationbetween the acquisition plane or volume of the surface scanner 102 andthe CT images can also be determined. As a result of the alignment, theacquisition plane or volume of the surface scanner 102 may be alignedwith the CT images in three-dimensional space, such that when thesurface scanner 102 acquires skin surface 105, the acquired skin surfacemay be effectively compared with the skin surfaces reconstructed from CTdata in process block 222 to produce a similarity measurement. After thealignment of the CT data with the treatment couch and patient, thetreatment delivery process 240 may begin.

According to one embodiment of the invention, treatment delivery process240 may be conducted as part of radiation treatment process 110, asillustrated in FIG. 3. Treatment delivery process 240 includes surfacetracking phase 310, which is followed by targeting phase 320. In thesurface tracking phase 310, a data model of the skin surface of thepatient is first acquired in process block 311. The data model is thenregistered with skin surfaces reconstructed from 4D CT data of thepatient in order to determine the temporal phase of the respiratorycycle at the time the data model was captured. Following process block312, execution of process block 321 in the targeting phase 320 takesplace. In process block 321, the location and orientation of a tumor orother volume within the patient is determined using previously acquired3D CT data corresponding to the temporal phase identified in processblock 312. Once the position of the tumor has been identified, a linearaccelerator (LINAC) may be moved so that its beam intersects a targetwithin the tumor or other volume, as provided in process block 322.Process blocks 311, 312, 321, and 322 may be repeated for the durationof the treatment delivery process 240 so that the location andorientation of the tumor may be continuously tracked and targeted by theLINAC. The process is described in further detail below.

Surface tracking phase 310 begins with process block 311, which providesfor the acquisition of a data model of a skin surface of the patient,such as skin surface 105 of the body of a patient 106. Surface scanner102 may perform the procedures of acquiring a data model of the skinsurface in motion, as provided by process block 311. As illustrated inFIG. 4A, these procedures, according to one embodiment, includeprojecting light onto the skin surface 401, capturing images of thesurface 402, and constructing a data model based on the images 403. Aspreviously mentioned, surface scanner 102 may be a system such as alaser scanning system or a digital photogrammetry system.

FIG. 4B illustrates components of a digital photogrammetry system thatmay be used as surface scanner 102, according to one embodiment of theinvention. Digital photogrammetry system 410 includes projector 411 andcameras 412 and 413. The digital photogrammetry system 410 may begin theskin surface acquisition process by projecting light onto the skinsurface 105, as provided in process block 401, using projector 411. Inone embodiment, projector 411 may project a pattern such as a pattern ofevenly spaced dots onto the skin surface 105. Alternatively, differenttypes of light patterns, such as lines or a grid, may also be projectedonto the skin. While the light pattern is being projected onto skinsurface 105, cameras 412 and 413, which may be situated at differentangles with respect to skin surface 105, may acquire images of skinsurface 105 by capturing the light reflected from skin surface 105 asprovided in process block 402. The images of skin surface 105 capturedby cameras 412 and 413 may then be used to triangulate positions ofpoints on the skin surface, since the images are taken from differentangles. The points can then be assembled into a three-dimensional modelof the skin surface in accord with process block 403.

In an alternative embodiment, surface scanner 102 may be a laserscanning system, such as laser scanning system 420 depicted in FIG. 4C.Laser scanning system 420 may include a laser 421 and a camera 422.Laser scanning system 420 initiates the acquisition of skin surface 105by projecting a point of laser light in a known direction onto skinsurface 105 using laser 421, as provided in process block 401. Camera422 may then be used to capture the location of the resulting point oflaser light reflected from skin surface 105 in accord with process block402. Subsequently, laser 421 may project a point of laser light onto adifferent location on skin surface 105, after which camera 422 may againcapture the location of the point of laser light. Thus, process blocks401 and 402 are repeated for every point on skin surface 105 to beacquired. In this manner, camera 422 may operate to capture a series ofpoints on skin surface 105. The location of each of these points inthree-dimensional space can then be triangulated using the knowndirection of the projected laser beam and the location of the point asseen and recorded by camera 422. The points, now having knowncoordinates in three-dimensional space, can subsequently be assembledinto a three-dimensional data model of skin surface 105, as provided inprocess block 403.

In other embodiments, methods other than digital photogrammetry or lasertriangulation may be used to acquire a data model of the skin surface.For example, the skin surface may be acquired using a method similar totime-of-flight laser range finding. Alternative embodiments may also useother techniques capable of acquiring the skin surface without activelyprojecting light onto the skin surface.

During the acquisition of skin surface 105, skin surface 105 may be inmotion. For example, skin surface 105 may rise and fall with therespiratory cycle of patient 106. Thus, the acquisition time requiredfor surface scanner 102 to acquire a complete scan of the skin surface105 may be sufficiently brief so that the scan data and resulting datamodel is not significantly affected by the motion of skin surface 105.

Once the scan of skin surface 105 is completed, the acquired data modelof skin surface 105 is registered with 4D CT data 103 by processor 101.The goal of the registration process is to identify one or more CTsurfaces, which are three-dimensional images of the skin surfacereconstructed from the 4D CT data 103, that are most similar to theacquired skin surface. A temporal phase corresponding to the acquiredskin surface may then be determined based on which of the CT surfacesare identified as most closely matching the acquired skin surface.

FIG. 5A illustrates a process according to one embodiment forregistering the acquired data model of the skin surface with the CTsurfaces in order to determine a temporal phase of the patient'srespiratory cycle, as provided in process block 312. FIG. 5B illustratesa series of three CT surfaces, 511, 513, and 514, that are to becompared with acquired skin surface 510. CT surfaces 511, 513, and 514correspond to temporal phases 521, 523, and 524, respectively, and mayhave been constructed from empirically sampled data. For example, CTsurfaces 511, 513, and 514 may have been reconstructed from dataacquired from a 4D CT scanner performing a scan on patient 106.Registration method 500 begins with process block 501, where asimilarity measurement is determined between the data model of the skinsurface and the CT surfaces. For example, a similarity measurement maybe calculated between two images, the first derived from a CT surfaceand the second derived from the data model of the skin surface. Thesimilarity measurement may be calculated by subtracting correspondingpixel values of the first image from the second image to form adifference image, then applying a pattern intensity function to thedifference image. The calculation of similarity measurements is known inthe art, therefore a more detailed description of the process forderiving a similarity measurement is not provided. Similaritymeasurements are described in detail in U.S. Pat. No. 7,187,792, U.S.patent application Ser. No. 10/652,786, and U.S. patent application Ser.No. 11/281,106. In accord with process block 501, a similaritymeasurement may be calculated between acquired skin surface 510 and eachof CT surfaces 511, 513, and 514. In other embodiments, a similaritymeasurement need not be calculated for all of the available CT surfaces.After the similarity measurement calculations, one or more of the CTsurfaces that most closely matches the data model is identified based onthe resulting similarity measurement, as provided in process block 502.For example, two CT surfaces, 511 and 513, may be identified that mostclosely match the acquired skin surface 510. Neither of CT surfaces 511or 513 may match acquired skin surface 510 exactly, since acquired skinsurface 510 may have been acquired during a temporal phase in thepatient's respiratory cycle that is different from the temporal phasesassociated with the two identified surfaces. For example, acquired skinsurface 510 may have been acquired during a temporal phase betweentemporal phases 521 and 523. Thus, following the completion of processblock 502, interpolation may be performed to generate a surfaceintermediate between CT surfaces 511 and 513 that more closely matchesacquired skin surface 510, as provided in process block 503. Theinterpolated skin surface may also correspond to a temporal phase moreclosely matching the temporal phase of acquired skin surface 510.According to one embodiment, several intermediate surfaces may begenerated by interpolation between the identified skin surfaces. Forexample, ten surfaces (not pictured) may be interpolated between CTsurfaces 511 and 513 which had been identified as most similar toacquired skin surface 510. Of these, interpolated surface 512 may matchacquired skin surface 510 with the best similarity measurement, asindicated by the “match” arrows 530. Thus, the temporal phase 522corresponding to interpolated surface 512 may be identified as thetemporal phase during which acquired skin surface 510 was captured.

The result of registration method 500 is that the temporal phase of thepatient's respiratory cycle, as of the time of the surface scan, isidentified. This temporal phase can later be used with the 4D CT data103 to determine the position of a target 107 with respect to the skinsurface 105.

An alternative embodiment for registering the acquired skin surface withthe CT surfaces in order to determine a temporal phase of the patient'srespiratory cycle, as provided in process block 312 is illustrated inFIG. 6A. FIG. 6B illustrates a series of three CT surfaces, 511, 513,and 514, that are to be compared with acquired skin surface 510. CTsurfaces 511, 513, and 514 correspond to temporal phases 521, 523, and524, respectively. Registration method 600, as illustrated in FIG. 6A,begins with process block 601, which provides for generation ofintermediate surfaces by interpolation between the CT surfaces, such asCT surfaces 511, 513, and 514, reconstructed from the 4D CT data 103.For example, during execution of process block 601, interpolatedsurfaces 601 and interpolated surface 612 are generated. Interpolatedsurfaces 601 and interpolated surface 612 correspond to intermediatetemporal phases between the temporal phases 521, 523, and 524corresponding to CT surfaces 511, 513, and 514, respectively. After thegeneration of the interpolated surfaces 601 and 612, execution proceedsto process block 602, where a similarity measurement is determinedbetween acquired skin surface 510 and each of the CT surfaces 511, 513,and 514, and the interpolated surfaces 601 and 612. In otherembodiments, calculation of a similarity measurement may not be requiredfor all of the CT surfaces and interpolated surfaces. After thesimilarity measurements have been calculated, execution proceeds toprocess block 603, where the surface having the best similaritymeasurement with the acquired skin surface 510 is identified. Forexample, interpolated surface 612 may be identified as having the bestsimilarity measurement with acquired skin surface 510, as indicated bythe “match” arrows 531. The temporal phase 522 corresponding tointerpolated surface 612 may then be identified as the temporal phaseduring which acquired skin surface 510 was captured.

FIG. 7 illustrates various surfaces along with corresponding tumorpositions, according to one embodiment of the invention. Otherembodiments of the invention may not identify positions of a tumor, butmay include positions of other objects, such as stones or lesions. For atumor position corresponding to a CT surface, such as tumor position 701corresponding to CT surface 511, the tumor position 701 identifies thelocation of the tumor relative to the CT surface 511 at the time oftemporal phase 521. Tumor position 701 may identify a different locationrelative to the skin surface as the location of the tumor than tumorposition 703 because the location of the tumor may change betweendifferent temporal phases. For example, the tumor may move as a resultof the patient's breathing or heartbeat.

Thus, if temporal phase 521 is identified in process block 312 as thetemporal phase most closely matching the temporal phase at which theacquired skin surface 510 was captured, then tumor position 701 can beused to locate the tumor relative to CT surface 511, as provided inprocess block 321. Since transformations between the CT data 103, whichincludes CT surface 511, and the treatment couch 109 have beendetermined during patient alignment phase 230, the transformations canbe used to locate the tumor in real space.

According to one embodiment of the invention, a tumor position can beinterpolated from two or more tumor positions, such as tumor positions701 and 703. This interpolation may take place during the execution ofprocess block 321. Tumor position 701 may indicate the location of thetumor at time T1, while tumor position 703 may indicate the location ofthe tumor at time T3. Thus, in order to determine the location of thetumor at time T2 intermediate between times T1 and T3, a tumor position702 is interpolated between tumor positions 701 and 703. Morespecifically, acquired skin surface 510 may be matched with interpolatedsurface 512, and the temporal phase of acquired skin surface 510 may bedetermined to be temporal phase 522 corresponding to interpolatedsurface 512. In order to determine the location of the tumor in relationto acquired skin surface 510 or interpolated surface 512, an additionaltumor location can be interpolated from existing tumor positions 701 and703. For example, interpolated tumor position 702 corresponding tointerpolated surface 512 may be interpolated from the tumor positions701 and 703, which correspond to CT surfaces 511 and 513 from whichinterpolated surface 512 was interpolated. Once the location of tumorposition 702 relative to interpolated surface 512 has been determined,tumor position 702 can be used to locate the tumor in real spacerelative to the patient's skin surface using the transformationsdetermined in patient alignment phase 230.

After the tumor position has been located in real space, processor 101may direct robotic arm 108 to move so that the beam of LINAC 104intersects a target 107, as provided in process block 322. The processof locating the tumor from the acquired skin surface 510 and 4D CT data103, then moving the LINAC 104 so that its beam intersects the target107 may be repeated so that the beam of LINAC 104 constantly intersectsthe target 107 for the duration of the treatment phase, despite themovement of target 107 due to the respiration, heartbeat, or othermovements of patient 106.

Alternatively, treatment delivery system 100 may be a type of systemother than a robotic arm-based system. For example, treatment deliverysystem 100 may be a gantry-based (isocentric) intensity modulatedradiotherapy (IMRT) system. In a gantry based system, a radiation source(e.g., a LINAC) is mounted on the gantry in such a way that it rotatesin a plane corresponding to an axial slice of the patient. Radiation isthen delivered from several positions on the circular plane of rotation.In IMRT, the shape of the radiation beam is defined by a multi-leafcollimator that allows portions of the beam to be blocked, so that theremaining beam incident on the patient has a pre-defined shape. Theresulting system generates arbitrarily shaped radiation beams thatintersect each other at the isocenter to deliver a dose distribution tothe target region. In IMRT planning, the optimization algorithm selectssubsets of the main beam and determines the amount of time that thepatient should be exposed to each subset, so that the prescribed doseconstraints are best met. In one particular embodiment, the gantry-basedsystem may have a gimbaled radiation source head assembly.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative embodiments, the methods and apparatus herein may be usedin applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials (e.g., motorblocks in the automotive industry, airframes in the aviation industry,welds in the construction industry and drill cores in the petroleumindustry) and seismic surveying. In such applications, for example,“treatment” may refer generally to the effectuation of an operationcontrolled by the treatment planning system, such as the application ofa beam (e.g., radiation, acoustic, etc.) and “target” may refer to anon-anatomical object or area.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a computer. The computer-readable medium mayinclude, but is not limited to, magnetic storage medium (e.g., floppydiskette); optical storage medium (e.g., CD-ROM); magneto-opticalstorage medium; read-only memory (ROM); random-access memory (RAM);erasable programmable memory (e.g., EPROM and EEPROM); flash memory; oranother type of medium suitable for storing electronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the communication medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

1. A method, comprising: acquiring a data model of a skin surface of abody based on light reflected from the skin surface, wherein the skinsurface undergoes movement; and registering the data model of thesurface with diagnostic imaging data to determine a matching temporalphase of the movement of the skin surface.
 2. The method of claim 1,wherein the diagnostic imaging data is four-dimensional diagnosticimaging data.